Electronic parts such as ceramic packages of ICs, quartz vibrators, image displays, etc have bed airtightly sealed with glass compositions having a softening point of 400° C. or lower. The glass compositions contain filler powder with a low thermal expansion so as to control a thermal expansion, in general. Glass compositions containing lead oxide as a main component have been used.
Due to environmental and safety regulations, materials containing harmful lead have been avoided. In plasma display panels (PDP), one of image display devices, lead free glass compositions whose main component is bismuth oxide have been employed as disclosed in Japanese Patent Pre-publication H10-139478 (Patent document No. 1). In electronic devices such as PDPs where a sealing temperature is relatively high such as 450 to 600° C. the lead free glass compositions containing bismuth oxide as the main component can be applied. However, in electronic devices such as IC ceramic packages or quartz vibrators where a sealing temperature is relatively low such as 420° C. or lower, the lead containing glass compositions are still employed. In order to lower the softening point of the lead containing glass compositions, fluorine is contained.
As lead free glass compositions having a softening point lower than that of the lead-free glass compositions, glass compositions there have been proposed in Japanese Patent Prepublication H07-69672 (Patent document No. 2), Japanese Patent Prepublication 2004-250276 (Patent document No. 3), Japanese Patent Prepublication 2006-342044 (Patent document No. 4), Japanese Patent Prepublication 2007-320822 (Patent document No. 5). The Patent document No. 2 discloses a glass composition whose main component is tin oxide. Patent documents No. 3 to 5 discloses glass compositions whose main component is vanadium oxide.
In recent years bismuth and antimony have been controlled as administrated substances, in addition to harmful lead. The glass compositions disclosed in patent document Nos. 1 and 4 contain bismuth, a glass composition disclosed in patent document No. 5 contains antimony, and glass compositions disclosed in patent document No. 2 and 3 do not contain lead, bismuth and antimony.
Patent documents:
                Patent document No. 1; JPH10-139478        Patent document No. 2; JPH7-69672        Patent document No. 3; JP2004-250276        Patent document No. 4; JP2006-342044        Patent document No. 5; JP2007-320822        
Recently, bismuth and antimony, in addition to lead, have taken up as administrated substances; these substances would be regulated similarly to lead in the feature. The glass compositions disclosed in patent document Nos. 1 and 4 contain bismuth and the glass composition disclosed in patent document No. 5 contains antimony. But, the glass composition disclosed in patent document Nos. 2 and 3 do not contain any of lead, bismuth and antimony.
When glass compositions disclosed in patent document No. 2 whose main component is tin oxide are heated in air, valence of tin changes from two to four, which deteriorates chemical stability such as moisture resistance and water resistance of the glass compositions. That is, it is hard to obtain airtight sealing with high reliability. Further, airtight sealing at 420° C. or lower is difficult to perform.
Although the glass compositions whose main component is vanadium oxide disclosed in patent document No. 3 can be used at a temperature of 400° C. or lower, a thermal expansion coefficient is quite large, and a large amount of low thermal expansion fillers such as expensive zirconium tungstate phosphate must be added. In addition, it is difficult to control thermal expansion. Further, a number of air bubbles may remain in the sealed portions so that airtightness of the sealed portions is insufficient.